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Page updated Sunday
24th 2003f August 2003
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Electric Bikes/Cars - PIC Group
"Electric Bike" talk by David Leigh and Peter Rosenthal, members of the South Australian Pic Users Group. ELECTRIC BIKES Two leading PIC Group members, David Leigh and Peter Rosenthal, described and demonstrated the many unique, ground-breaking features of their electrically powered bikes at our July meeting. Both bikes are fairly standard road bikes fitted with rechargeable battery powered electric motors combined with control and transmission systems clamped onto the bikes in such a way that the bikes can be restored to normal if they ever need be (although I doubt if they ever will). Both bikes can still use their peddles in the normal way but can be used in conjunction with electric motors more or less depending on the situation. Generally the bikes can run entirely on motor power for cruising on flat ground and only need peddle assistance going up hills or for going faster. On most road bikes, when you are free-wheeling, the peddles and chain are stationary and a ratchet in the rear wheel (along with the gears) allows the rear wheel to turn freely. Peter uses that method but has an added rear wheel sprocket and chain connected to the motor. This allows Peter to free-wheel, to peddle assist the motor, or even just use the peddles with the motor power turned off. 
Using a different approach, David has three ratchets and three sprocket, but only one chain in his transmission system. There is the usual rear wheel ratchet in addtion to a somewhat unusual peddle ratchet to allow free-wheeling and a ratchet in the motor drive to allow the motor to remain stationary without causing drag on the system when no power is being applied to the motor. David can free-wheel, peddle assist the motor, or even just peddle with the motor turned off in a similar way to Peter. Where motors are concerned, David has gone to the extent of designing and building a very efficient, compact, light-weight 500 watt motor using 14 rare earth magnets in the external rotor and 12 electronically switched internally located stationary field coils. The coil switching is done with very low on-resistance FETs controlled by - yes, you guessed it - a PIC microprocessor (PIC 12F675). This super light-weight motor is only about the size of a fist and, amazingly, can deliver a continuous 500 watts at 24 volts or 375 watts at the 12 volts he normally uses. This motor is by itself an outstanding bit of design work. Apart from the motor controller, David uses more microprocessors in the handle-bar motor controls and the battery monitoring, plus a few more for light controls (and that's not counting the ones in his mobile phone, GPS, Palm Pilot, watch, etc.!) Peter has used a more conventional commercially-made motor rescued from a photocopier. It is a fairly standard brush switched, commutator, universal DC motor delivering about 200 watts. So far Peter has avoided any sophisticated controls, but would like to include them when he starts adding solar power panels as a lead up to the World Solar Challenge. When it comes to batteries, Peter has spent a lot of time looking into the many types for ones with the most suitable characteristics. He has settled for the time being for lead-acid, sealed, deep cycle 12 volt 14 Amp-Hour batteries, but would be more than willing to swap these for more suitable and much more expensive types when he enters the World Solar Challenge in the near future. David has used 12 nickel metal hydride cells of 12 amp-hours, but admits this is a weakness in the system due to their not-so-good deep cycling characteristics compared to the more expensive "exotic" types. The front runner for the ideal battery at the moment is the lithium ion battery. They have about the best weight-volume-energy characteristics combined with among the best recharging efficiencies (conversion of charging energy into stored energy) of any cells and if cost wasn't a factor they would be Peter and David's first choice. While David and Peter have been looking over each others shoulders during the development of these two bikes it is interesting that their approaches have been fairly different even though the end products give much the same outstanding performances. It is also worth noting that the approximately 200 watts that these motors output is comparable to reasonably fit cyclists peddling without motor assistance (eg. Ian Fisk - Hi, Fisky). Thanks guys for a very interesting look at what could be, or should be, in an energy starved world, the future of a lot of personal transport. Also, good luck Peter in the World Solar Challenge. . . . . Rick Matthews
Spec sheet for Davids bike; |
